DE19549547B4 - Thixocasting semi-molten casting material and its mfr. - the material comprising composite solid phases each having liq. and solid phases, and single solid phases - Google Patents

Abstract

Thixocasting semi-molten casting material having solid and liquid phases coexisting in it comprises a number of composite solid phases each having a liquid phase region and a solid phase region enclosing the liquid phase region, and a number of single-solid phases having no liquid phase region. The composite solid phases and the single solid phases are mixed as the solid phases in an outer layer portion of the semi-molten casting material. If a liq. enclosure rate P of one of the composite solid phases is defined as: P = (B/(A+B)) x 100 (%) (where A = sectional area of the solid phase region; and B = sectional area of the liquid phase region), and the liq. enclosure rate P of the single solid phase is defined as: P = O (%), and if N number of groups are selected from a class of the solid phases in the outer layer portion so as to include a no. of the solid phases, the average values Ml to Mn of liq. enclosure rates P1, P2....Pn-1 and Pn of an n no. of solid phases in first to N-th gps. are represented by M1=(P1+P2....+Pn-1+Pn)/n to Mn=(P1+P2....+Pn-1+Pn)/n and an average value Mm=(M1+M2....+Mn-1+Mn)/N of the average values M1 to Mn is in a range of Mm = at least 20%. Prodn. of the material is also claimed.

Description

The The present invention relates to a semi-molten thixocasting casting material.

At the Carry out a thixocasting process For example, a procedure is used which involves exposing a casting material contains a heat treatment, around a semi-molten (semi-molten) casting material which produces a solid phase (a substantially solid) Phase, etc.) and a liquid phase which coexist therein, and loading the semi-molten casting material into a cavity in a mold under pressure and solidifying the semi-molten casting material below the pressure.

at the heat treatment becomes the solid phase content in the semi-molten casting material set so firmly, the thixocasting process is performed gently. At such a solid phase content is the flow resistance of the semi-molten casting material decreases and therefore it is likely that the following disadvantage occurs: Part of the semi-molten casting material flows out or the semi-molten casting material is deformed.

One The method used in the prior art is the fitting of the casting material in a ring before heat treatment, to drain and to prevent deformation by the ring (see for example U.S. Patent No. 4,712,413).

This However, prior art method is accompanied by the problem, the existence Requirement for operations arises, which include the fitting of the casting material in the ring, removing the ring from the casting material and removing a solidified metal portion which deposits on the ring has, which leads to a complicated casting process.

Out metallographic and economic The point of view is the casting material generally by using a stirred continuous casting process produced; in the method for producing the casting material However, it is not avoided that an outer layer portion dendrites which has an outer circumference a main body section of the casting material exist around. The dendrites cause the pressure to load the semi-molten casting material increased in the cavity is going to get the full one Loading the semi-molten material into the cavity to complicate and therefore the dendrites in the casting material are undesirable.

Therefore become conventional the following procedures are used: a method of removing the Dendrites through a dendrite trap, which is mounted in a mold is (see Japanese Patent Publication No. 51703/90), and a method for exposing the casting material a cutting operation for removing the outer layer portion.

The first method for removing the dendrites by a dendritic trap, which is mounted in the mold is that causes the Structure of the mold complicated and brings an increase in costs. The second method for cutting the outer layer portion brings an increase in work steps and a deterioration in productivity.

It An object of the present invention is a semi-molten one Gießmateriah of the type described above, which is a good one dimensional stability and wherein by specifying the structure of the outer layer portion in the semi-molten state, it can be prevented from flowing out and deforming becomes.

In order to achieve the foregoing object, according to the present invention, there is provided a semi-molten thixocasting molding material having solid and liquid phases coexistent therein, wherein the material comprises a plurality of composite solid phases each having a liquid phase region and a solid phase region surrounding the liquid phase region , and a plurality of individual solid phases having no liquid phase region, wherein the composite solid phases and the individual solid phases are mixed as the solid phases in an outer layer portion of the semi-molten casting material, and wherein when a liquid inclusion rate P is defined by one of the composite solid phases as P = {B / (A + B)} × 100 (%), where A is a sectional area of the solid phase area and B is a sectional area of the liquid phase area, and wherein the liquid phase inclusion rate P of the single solid phase is defined as P = 0 (%), and when a number N of groups of a class of the solid phases in the outer layer portion is selected to include a plurality of the solid phases, averages M ₁ to M _{N of} the liquid inclusion rates P ₁ , P ₂ ... P _n-1 and P _{n of} a number n of solid phases in first through N-th groups are represented by M ₁ = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n to M _N = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n and an average M _M (= (M ₁ + M ₂ ... + M _N-1 + M _N ) / N) of the mean values M ₁ to M _N in the range of M _M ≥ 20%.

In addition, according to the present invention, there is provided a semi-molten thixocasting molding material having solid and liquid phases coexistent therein, wherein the solid phases existing in an outer layer portion of the molding material are a plurality of composite solid phases each having a liquid phase region and a liquid phase region And wherein, when a liquid inclusion rate P of one of the composite solid phases is defined as P = {B / (A + B)} × 100 (%), where A is a sectional area of the solid phase region and B is a sectional area of the liquid phase region and when a number N of groups of a compound of the composite solid phases in the outer layer portion is selected to comprise a plurality of the composite solid phases, averages M ₁ to M _{N of} the liquid inclusion rates P ₁ , P ₂ ,. P _{n- 1} and P _{n of} an Num of the composite solid phases in first to Nth groups are represented by M ₁ = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n to M _N = (P ₁ + P ₂ . .. + P _n-1 + P _n ) / n and an average value M _M (= (M ₁ + M ₂ ... + M _{N- 1} + M _N ) / N) of the mean values M ₁ to M _N in the range of M _M ≥ 20% is set.

If the connected solid phases and the individual solid phases in the outer layer section exist, or if only the connected solid phases in the outer layer portion exist, then the amount of the liquid phase becomes the solid phase around according to the crowd the liquid phase enclosed in the connected solid phase reduced.

Therefore, when the average value M _M relating to the liquid phase inclusion rate P in the outer layer portion is set in the range of M _M ≥ 20%, the apparent solid content in the outer layer portion is increased more than an actual solid phase content according to the average value M _M , Thus, it is possible to improve the dimensional stability (dimensional stability) of the semi-molten casting material and to prevent the outflow and deformation.

However, if the average value M _{M is} less than 20%, the outflow of the liquid phase occurs, resulting in a sudden increase in weight loss.

to Preparation of a semi-molten thixocasting casting material is a process comprising the steps of exposing the thixocasting material, comprising an outer layer portion with the dendrites around an outer circumference a main body section around, a heat treatment, to a semi-molten casting material to produce, which has solid and liquid phases, the coexist in which the dendrites transform into spherical solid phases will increase by the temperature of the outer layer portion preferred with respect the main body section, around the outer layer section into a semi-molten state.

If the outer layer section in the casting material brought by heating in the semi-molten state, then can in the outer layer section existing dendrites transformed into the spherical solid phases become. In this case, the semi-melting of the main body portion occurs only after the outer layer section on and therefore can be an extension the heating time for the Main body portion be avoided to coalescence (growing together) or a Swelling of the metallographic structure of the main body portion to prevent.

It is thus possible the semi-molten casting material Completely and gently invade the cavity under a low boost pressure, a good cast product to create. additionally can not the disadvantages of complicating the structure of the mold and the increase in the steps as in the prior art occur.

The The foregoing and other objects, features and advantages of the invention will become apparent from the following description of preferred embodiments Evidently, when used in conjunction with the accompanying drawings is looked at.

1 Fig. 10 is a vertical sectional view of a first example of a press molding apparatus;

2 Fig. 10 is a photomicrograph showing the metallographic structure of an outer layer portion in a first example of an aluminum alloy material;

3 Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in a second example of an aluminum alloy material;

4 Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in a third example of an aluminum alloy material;

5A Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in a first example of a semi-molten aluminum alloy material;

5B is a reproduction of an essential section which is in 5A is shown;

6A Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in a second example of a semi-molten aluminum alloy material;

6B is the reproduction of an essential in 6A section shown;

7A Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in a third example of a semi-molten aluminum alloy material;

7B is a reproduction of an essential in 7A section shown;

8th Fig. 12 is a graph showing the relationship between the average value M _M relating to the liquid phase inclusion rate P and the weight loss;

9 Fig. 10 is a vertical sectional view of a second example of a press molding apparatus;

10A Fig. 10 is a photomicrograph showing the metallographic structure of a main body portion in a fourth example of an aluminum alloy material;

10B Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in the fourth example of the aluminum alloy material;

11A Fig. 10 is a micrograph showing the metallographic structure of a main body portion in a fourth example of a semi-molten aluminum alloy material;

11B Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in the fourth example of the semi-molten aluminum alloy material;

12A Fig. 10 is a photomicrograph showing the metallographic structure of a main body portion in a fifth example of a semi-molten aluminum alloy material;

12B Fig. 10 is a photomicrograph showing the metallographic structure of an outer layer portion in the fifth example of the semi-molten aluminum alloy material;

13 Fig. 12 is a graph showing the relationship between the difference a-b between area rates of α-Al crystals and the boost pressure;

14A Fig. 10 is a micrograph showing the metallographic structure of a main body portion in a sixth example of a semi-molten aluminum alloy material;

14B Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in the sixth example of the semi-molten aluminum alloy material;

15A Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in a seventh example of an aluminum alloy material;

15B is a reproduction of an in 15A shown essential section;

16 Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in a seventh example of a semi-molten aluminum alloy material;

17 Fig. 10 is a photomicrograph showing the metallographic structure of an aluminum alloy casting produced by using the seventh example of the aluminum alloy material;

18A Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in an eighth example of an aluminum alloy material;

18B is a reproduction of an in 18A shown essential section;

19 Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion in an eighth example of a semi-molten aluminum alloy material;

20A Fig. 11 is a photomicrograph showing an example of the metallographic structure of an aluminum alloy casting produced by using the eighth example of an aluminum alloy material; and

20B Fig. 11 is a photomicrograph showing another example of the metallographic structure of an aluminum alloy casting produced by using the eighth example of the aluminum alloy material.

I. Semi-molten Thixocasting casting

The 1 shows a first example of a Preßgießeinrichtung 1 , which is used to make a cast product in a thixocasting process. The Preßgießeinrichtung 1 includes a stationary mold 2 and a movable mold 3 which are vertical mating surfaces 2a respectively. 3a exhibit. A casting cavity 4 is between the two mating surfaces 2a and 3a educated. A chamber 6 in which a semi-molten casting material 5 is arranged, is in the stationary form 2 formed and communicates with a lower portion of the cavity 4 through a passage 7 in connection. A sleeve 8th is horizontal at the stationary form 2 attached and stands with the chamber 6 in conjunction, and a plunger 9 is slidable in the sleeve 8th taken up for sliding into and as the chamber 6 , The sleeve 8th has a material inlet 10 in an upper portion of its peripheral wall.

In a casting process is a casting material 5 is cut from a long, high quality continuous cast product made in a stirred continuous casting process and then the casting material 5 disposed in a heating coil in an induction heater and therein for producing a casting material 5 heated in a semi-molten state, which product has solid and liquid phases. In this case, the solid phase content is set in the range of 50% (inclusive) to 60% (inclusive).

Thereafter, the semi-molten casting material 5 in the chamber 6 arranged and the piston 9 is actuated to cause the semi-molten casting material 5 through the passage 7 in the cavity 4 is loaded while it is pressed. Then, a pressing force is applied to the semi-molten casting material 5 which exerted in the cavity 4 is filled by the plunger 9 held at one end of the stroke, whereby the semi-molten casting material 5 is solidified under such an applied pressing pressure to provide a cast product.

The Table 1 shows the composition of a hypoeutectic (hypoeutectic) Aluminum alloy material as a casting material.

Table 1

Three Alloy materials I, II and III with those shown in Table 1 Composition and with a diameter of 76 mm and a length of 85 mm have been prepared.

The 2 FIG. 12 is a micrograph showing the metallographic structure of an outer layer portion of the aluminum alloy material 2. You can go out 2 recognize that the outer layer portion is formed from swelling grown dendrites. Each of the dendrites is of the type α-Al, and a portion which fills the region between the dendrites is eutectic Al-Si.

The 3 Fig. 10 is a micrograph showing the metallographic structure in an outer layer portion of the aluminum alloy material II. You can go out 2 recognize that the outer layer portion is formed of dendrites, but the Dendritarmabstand is greater than that in the aluminum alloy material I. Similarly, each of the dendrites of the type α-Al, and a portion which fills the area between the dendrites is eutectic Al-Si.

The 4 Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion of the aluminum alloy material III. You can go out 2 recognize that the outer layer portion has a spherical structure. Each of the spherical portions is an α-Al crystal, and a portion which fills a region between spherical portions is likewise eutectic crystalline Al-Si.

Then is the aluminum alloy material I in the heating coil in the induction heater has been arranged and is then under conditions of a frequency of 1 kHz and an excitation time of 7 minutes (Issue 90 % for the first three minutes, issue 52% for the next 1 minute and issue 37 % for the last 3 minutes) until the solid phase reaches 60, thereby a semi-molten aluminum alloy material I has been produced is. After that, the metallographic structure of the semi-molten Aluminum alloy material I fixed by a quenching method Service.

The 5A FIG. 12 is a micrograph showing the metallographic structure of an outer layer portion of the semi-molten aluminum alloy material I and FIG 5B is a reproduction of an in 5A shown essential section.

In the 5A and 5B Each of the solid sections is a solid phase Sp, and a section which fills a region between the solid phases Sp corresponds to a liquid phase Lp. The fixed phases Sp are a mixture of a plurality of composite solid phases Sc each having a liquid phase region La and a solid phase region Sa including the liquid phase region La, wherein a plurality of individual solid phases Ss has no liquid phase region La.

Of the Solid phase region Sa and the single solid phase region Ss of the composite solid phase Sc include α-Al crystals, and the liquid phase region La and the liquid phase area Lp of the composite solid phase Sc include eutectic Al-Si.

The liquid phase inclusion rate P of one of the composite solid phases Sc is represented by P = {B / (A + B)} × 100 (%), and the liquid phase inclusion rate P of the single solid phase Ss is represented by P = 0 (%), where A is a sectional area of the solid phase area Sa and B is a sectional area of the liquid phase area La (a sum of the sectional areas of all the liquid phase areas La enclosed by the solid phase area Sa). When a number N of groups of a class of solid phase Sp (including the composite solid phases Sc and the single solid phase Ss) in the outer layer region are selected to include a plurality of solid phases Sp, averages M ₁ to M _{n of} the liquid phase inclusion rates P ₁ , P ₂ , ... P _n-1 and P _{n of} a number n of liquid phases Sp in the first to the N-th group represented by M ₁ = (P ₁ + P ₂₎ + P _n-1 + P _n ) / n, ... and M _N = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n, and the mean value M _{M of} these mean values M ₁ to M _N (= (M ₁ + M ₂ ... + M _N-1 + M _N ) / N) is set in the range of M _M ≥ 20.

In the outer layer of the semi-molten aluminum alloy material I, the average value M _M relating to the liquid phase inclusion rate P has been determined in a manner which will be described below. (i) As in 5B shown, two or more (two in the illustrated embodiment) first and second straight lines C and D are drawn on the microscope photograph, and two (N) groups have been selected from a resulting class of solid phases Sp such that they are three liquid Include phases Sp. (ii) Liquid phase influence rates P ₁ , P ₂ and P _{3 of} the three (number n of) composite solid phases Sc in the first group, which are crossed by the first straight line C, have been determined, and a first average value M ₁ (= (P ₁ + P ₂ + P ₃ ) / 3) has been calculated. In this case M _{1 was} equal to 19%. (iii) Liquid phase inclusion rates P ₄ , P ₅ and P _{6 of} the three (number n of) composite solid phases Sc in the second group crossed by the second straight line D have been determined, and a second average M ₂ (= P ₄ + P ₅ + P ₆ ) / 3) has been calculated. In this case M ₂ was 21%. (iv) An average of the first and second mean values M ₁ and M ₂ , ie M _M (= (M ₁ + M ₂ ) / 2), has been calculated as the mean value M _M.

Thus, it has been made clear that the average value M _M relating to the liquid phase inclusion rates P in the outer layer portion of the semi-molten alloy material I was 20% (M _M = (19% + 21%) / 2 = 20%. ).

The 6A FIG. 13 is a photomicrograph showing the metallographic structure of an outer layer portion of the semi-molten aluminum alloy material II and FIG 6B is a reproduction of an in 6A shown essential part.

In this case, a first average M ₁ (= (P ₁ + P ₂ ... P ₉ + P ₁₀ ) / 10) (assuming P ₁ and P ₅ = 0) was 1.7%, and a second average M ₂ (= (P ₁₁ + P ₁₂ ... P ₁₅ + P ₁₆ ) / 6) was equal to 1.8%. Thus, it has been made clear that the average value M _M relating to the liquid phase inclusion rates P in the outer layer portion of the semi-molten aluminum alloy material II was 1.8% (M _M = (1.7 + 1.8%) / 2 = 1.8%).

The 7A FIG. 12 is a micrograph showing the metallographic structure of an outer layer portion of the semi-molten aluminum alloy material III, and FIG 7B is a reproduction of an in 7A shown essential part.

In this case, a first mean M ₁ (= P ₁ + P ₂ ... P ₈ + P ₉ ) / 9) (assuming P ₄ , P ₅ and P ₆ = 0) was equal to 0, 8, and a second average M ₂ (= (P ₈ + ₁₀ ... P ₁₄ + ₁₅ ) / 7) (assuming P ₁₁ and P ₁₃ = 0) was equal to 0.2%. It has thus been made clear that the average value M _M relating to the liquid phase inclusion rates P in the outer layer portion of the semi-molten aluminum material III was 0.5% (M _M = (0.8% + 0.2 %) / 2 = 0.5%).

Table 2 shows the relationship between the average value M _M relating to the liquid inclusion rate P and the weight loss in the outer layer portions of the semi-molten alloy materials I, II and III and other semi-molten alloy materials IV, V and VI. In the outer layer portion of the semi-molten alloy material IV, only single solid phases Ss exist and there are no composite solid phases Sc.

Table 2

The 8th FIG. 12 is a graph showing the relationship between the average value M _M (%) relating to the liquid inclusion rates P and the weight loss based on Table 2. How out 8th can be reduced, the weight loss can be reduced to 10 wt .-% or less by the average value M _{M is set} in the range of M ≥ 20%.

The present invention comprises a semi-molten thixocasting casting material in which the solid phases Sp existing in the outer layer portion are a plurality of composite solid phases Sc each having a liquid phase region La and a solid phase region Sa containing the liquid phase region La includes. In this case, the liquid phase inclusion rate P of one of the composite solid phases Sc is represented by P = {B / (A + B)} × 100 (%), where A is a sectional area of the solid phase area Sa and B is a sectional area of the liquid phase area La. When a number N of groups of a class of composite solid phases Sc in the outer layer portion are selected to comprise a plurality of composite solid phases Sc, then average values M ₁ to M _{n of} the liquid phase inclusion rates P ₁ , P ₂ ,. P _n-1 and P _{n of} a number n of the composite solid phases Sc in the first to the N-th group represented by M ₁ = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n, ... and M _N = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n, and the mean value M _{M of} these mean values M ₁ to M _N (= (M ₁ + M ₂ ... + M _N-1 + M _N ) / N) is set in the range of M _M ≥ 20%.

II. Production of semi-molten Thixocasting casting material

The 9 shows a Preßgießeinrichtung 1 , which is used to make a cast product in a thixocasting process. The Preßgießeinrichtung 1 includes a stationary mold 2 and a movable mold 3 which surfaces vertically matching one another 2a respectively. 3a exhibit. A casting cavity 4 is between the two matching surfaces 2a and 3a educated. A chamber 6 in which a semi-molten casting material 5 is arranged is in the stationary form 2 trained and stands with the cavity 4 through a passage 7 in connection. A sleeve 8th is arranged in an ascending manner on the stationary mold and communicates with the chamber 6 in conjunction, and a plunger 9 is slidable in the sleeve 8th taken for sliding into and out of the chamber 6 ,

(A) Relationship between the casting material and the heater

(Example 1)

Under Use of a molten material which has a hypoeutectic Aluminum alloy composition shown in Table 3 is a round rod-shaped molded product with a diameter of 76 mm in the stirred continuous casting process been prepared.

Table 3

An aluminum alloy material as the casting material has been cut off from the round rod-like molded product with a length of 100 mm and has been examined with respect to its metallographic structure, resulting in the in the 10A and 10B results shown.

The 10A FIG. 12 is a micrograph showing the metallographic structure of a main body portion, and FIGS 10B Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion existing around an outer circumference of the main body portion.

How out 10A As is apparent, the main body portion has a large number of spherical α-Al crystals and eutectic crystals each filling a region between the spherical α-Al crystals. How out 10B As is apparent, the outer layer portion has a large number of dendrites as well as eutectic Al-Si crystals, each of which has a region between the dendrites fill up. The dendrites are formed from α-Al crystals.

In In this case, the area rate a of the α-Al crystals in the outer layer section equal to 86% and the area rate b of the α-Al crystals in the main body portion is equal to 75%. These area rates a and b are measured using an image analysis system, etc. Service.

The Aluminum alloy material I is disposed in an induction heating furnace and then is an induction heating under a state of Frequency f of 1 kHz (constant) and an excitation time of 7 minutes been subjected (90% issue for the first 3 minutes, issue 50% for the next 1 minute and spending 37% for the last 3 minutes).

In In this case, the electrical resistance of the outer layer portion lower than that of the main body portion due to Fact that the area rate a of the α-Al crystals in the outer layer section is higher as the area rate b of the α-Al crystals in the main body portion and the α-Al crystal has a good conductivity. Therefore, in the outer layer portion occurs a remarkable skin effect on, which causes the temperature of the outer layer section across from the main body section preferably increased is to obtain a semi-molten state in which solid and liquid Phases are coexistent. A subsequent induction heating causes that the Temperature of the main body section elevated so that this also assumes a semi-molten state in which solid and liquid Phases are coexistent.

In this way, the aluminum alloy material was heated to 575 ° C, which is a pourable temperature, and then the metallographic structure in the semi-molten state was fixed by a quenching method and examined, resulting in the 11A and 11B results shown.

The 11A FIG. 12 is a micrograph showing the metallographic structure of a main body portion, and FIGS 11B Fig. 10 is a micrograph showing the metallographic structure of an outer layer portion.

Like from the 11B As can be seen, it can be seen that the dendrites in the outer layer portion have been converted into spherical solid phases by the semi-melting. In this case, a mean diameter D of the spherical solid phases of the α-Al crystals is 150 μm. Here, the term "average diameter" is defined as an average of the lengths of the longest portions of all the spherical solid phases on the microscope photograph. This also refers to the mean diameter D, which will be described below.

Like from the 11A is apparent, the main body portion in this case also has a spherical structure, and a mean diameter D of the spherical solid phases of the α-Al crystals is equal to 120 microns. The reason why the fine metallographic structure is obtained in the main body portion in this manner is that the half-melting of the main body portion occurs after that of the outer layer portion, and therefore, an increase in the heating time of the main body portion is avoided to cause swelling or coalescence to avoid the metallographic structure.

Then the mold temperature is in an in 9 have been set to 250 ° C and the semi-molten alloy material I (by the reference numeral 5 referred to) obtained after heating is in the chamber 6 been arranged. The plunger 9 has been actuated to the semi-molten alloy material I in the cavity 4 to load. In this case, the pressure for loading the semi-molten alloy material I (the pressure piston 9 etc. applied pressure) equal to 8 MPa. Then, a pressing force has been exerted on the semi-molten alloy material I, which is in the cavity 4 was filled by the plunger 9 at a stroke end, whereby the semi-molten alloy material I has been solidified under such a pressure to provide an aluminum alloy cast product.

following are various aluminum alloy materials II, III, IV, V and VI having the composition shown in Table 3 and what different rates a and b of the α-Al crystals in the outer layer section and the main body portion had and the same size as previous described.

Then, each of the aluminum alloy materials II, III, IV, V and VI is in the induction heating furnace and heated under the same conditions as those described above. Thereafter, the metallographic structure in the semi-molten state was produced at a pourable temperature of 575 ° C in the same manner and then measured.

Using the aluminum alloy materials II, III, IV, V and VI after being heated and using the in 9 In the press molding apparatus shown, various aluminum alloy castings are produced by the same casting operation as described above.

The Table 4 shows the area rates a and b of the α-Al crystals in the outer layer section and the main body portion of each of the aluminum alloy materials I, II, III, IV, V and VI, the difference a - b between the area rates a and b, the shape of the solid phase in the semi-molten outer layer portion and the boost pressure during of the casting.

Table 4

The 12A and 12B are micrographs showing the metallographic structure of the semi-molten aluminum alloy material VI. The 12A corresponds to the main body section and the 12B corresponds to the outer layer section.

Like from the 12B As can be seen, the solid solid phase occurs due to the aggregation of the spherical solid phases in the outer layer portion. You can go out 12A recognize that the main body portion has a spherical structure.

If the dendrites in the outer layer section, as in the aluminum alloy materials I, II, III and IV in Table 4, in the spherical be transformed into solid phases, then the boost pressure during the casting at a substantially constant value, e.g. 8 to 9 MPa be fixed and can be lowered. Each of the aluminum castings, which consists of the aluminum alloy materials I, II, III and IV had a fine metallographic structure and had no defects, such as Cutouts and cavities, in himself and was good.

If on the other hand, the dendrites in the outer layer portion not in the spherical solid phases, as in the aluminum alloy materials V and VI in Table 4, then the boost pressure as a result increased from it, that very much probably produces defects in the aluminum alloy casting were.

The 13 FIG. 12 is a graph showing the relationship between the difference a-b between the area rates of α-Al crystals and the boost pressure based on Table 4, wherein Dots I, II, III, IV, V and VI denote the aluminum alloy materials I, II, III, IV, V and VI respectively.

How out 13 As is apparent, it is desirable that the difference a-b between the area rates of the α-Al crystals be in the range of 5% ≦ a-b ≦ 15% in order to lower the boost pressure.

Comparative Example 1

The aluminum alloy material of Example 1 was placed in an electric resistance furnace and heated to 575 ° C for a long period of time under a heating time of 3 hours, at which temperature the material was in a semi-molten state and solid and liquid phases exhibiting coexistence in which it was at a pourable temperature. Thereafter, the metallographic structure in the semi-molten state has been fixed by a quenching method and has been investigated, resulting in the in the 14A and 14B results shown.

The 14A FIG. 11 is a photomicrograph showing the metallographic structure of the main body portion and FIG 14B Fig. 10 is a micrograph showing the metallographic structure of the outer layer portion.

Like from the 14B As can be seen, it can be seen that the dendrites in the outer layer portion have been transformed by semi-melting into spherical solid phases. In this case, a mean diameter D of the spherical solid phases of the α-Al crystals is equal to 160 μm, and the spherical solid phase is relatively fine.

On the other hand, how, out 14A Further, the main body portion has a spherical structure, but in this case, the average diameter D of the spherical solid phases of the α-Al crystals is 210 μm. The reason why the metallographic structure of the main body portion was coalesced or swelled in this manner is that the aluminum alloy material IIa has been heated for a long period of time.

Then, using the semi-molten alloy material II after it has been heated and using the press-molding device 1 , what a 9 1, an aluminum alloy casting IIa has been produced by the same casting operation as in Example 1.

Test pieces are from the aluminum alloy casting I using the aluminum alloy material I of the example 1, and the aluminum alloy cast product IIa of Comparative Example 1 has been prepared. Then each one is the test pieces T6 treatment (comprising heating to 540 ° C for 5 hours, a water-cooling and heating to 170 ° C for 5 hours), and then subjected to a tensile test, resulting in the in Table 5 results shown Has. In Table 5, the test pieces I and IIa correspond to the aluminum alloy castings I or IIa.

Table 5

As from Table 5, the test piece I of Example 1 has a high Strength and high ductility (ductility) on. This is the fact that the Dendrites in the outer layer section in spherical solid phases have been transformed and that the spherical structures of the outer layer portion and the main body portion were fine.

on the other hand has the test piece IIa in Comparative Example 1 low strength and low ductility in comparison to the test piece I rely on the fact that the spherical structure of the main body section coalesced or swollen.

(Example 2)

The aluminum alloy material I of Example 1 was placed in an induction heating furnace and subjected to a first (primary) induction heating step in a coil of the induction heating furnace under conditions of a frequency f ₁ of 2 kHz (constant) and an energization time of 3 minutes (output 90%). ,

there is a skin effect, corresponding to that of Example 1, in remarkably occurred, and therefore the temperature of the outer layer section in terms of the temperature of the main body portion preferably increased been so that the outer layer section has assumed a semi-molten state in which solid and liquid Phases coexist.

Then, the aluminum alloy material I undergoes a second (secondary) induction heating step in the coil under conditions of a frequency f ₂ of 1 kHz (constant) and an energization time of 4 minutes (output 50% for the 1 minute and output 37 for the next 3 minutes) were.

This has caused that Temperature of the main body section has been raised and this one semi-molten state has assumed in which solid and liquid phases coexist.

In In this way, the aluminum alloy material I is heated to 575 ° C what a pourable Temperature is. After that, the metallographic structure is semi-molten Condition fixed using a quenching method and has been studied. As a result, it has become clear that the Dendrites in the outer layer section in spherical solid phases have been transformed. In this case was one average diameter of the spherical solid phases of the α-Al crystals same 160 μm.

Of the Main body portion has also spherical Structures exhibited. In this case the mean diameter was the spherical one solid phases of the α-Al crystals equal to 120 μm.

Then, using the semi-molten aluminum alloy material I after it has been heated and using the press-molding device 1 , what a 9 1, an aluminum alloy casting was produced by the same casting as in Example 1. This is referred to as Example 1.

Likewise, using the aluminum alloy material I, two aluminum alloy castings have been manufactured under the same conditions as those described above except that the frequency f _{1 has} been changed in the first induction heating step. These are referred to as examples 2 and 3, respectively.

Table 6 shows the relationship between the frequencies f ₁ and f ₂ in the first and second induction heating steps and the boost pressure. For comparison, data relating to the aluminum alloy material I in Example 1 is shown as that of Example 4 in Table 6.

Table 6

As is apparent from Table 6, when the frequency f ₁ in the first induction heating step is set higher than the frequency f ₂ in the second induction heating step as in Examples 1 to 3, the spherical solid phases resulting from the transformation of the dendrites can be set , are brought into a shape closer to a spherical shape as compared with those of Example 4, and therefore, the boost pressure is lower than in Example 9.

The frequency f ₁ in the first induction heating step is suitably in the range of 0.8 kHz <f ₁ ≦ 50 kHz for preferentially raising the temperature of the outer layer portion. When the frequency f _{1 is} lower than 0.8 kHz or higher than 50 kHz, the efficiency of a heating oscillation circuit is low, and therefore this frequency level is not practical.

The frequency f ₂ in the second induction heating step is suitably in the range of 0.8 kHz <f ₂ ≦ 5 kHz for the uniform heating of the main body portion. If the frequency f _{2 is} lower than 0.8 kHz, it is also not practical. On the other hand, when f ₂ > 5 kHz, the outer layer portion is preferably heated, and therefore, the entire main body portion can not be heated in a uniform manner. The reason why the frequency f _{1 is defined} higher than 0.8 kHz is that the relation f ₁ > f _{2 is} satisfied.

On the other hand, f the frequency of ₁ in the first induction heating step is lower than the frequency f ₂ during the second induction heating step, namely, f ₁ <f _2, the following disadvantages occur: It is supported oxidation of the outer layer portion, so that a thick oxide film is formed, and a part of the outer layer portion flows out, resulting in a reduced yield.

(B) Average diameter the spherical one solid phases in the outer layer portion in the semi-molten state

(Example 1)

One Aluminum alloy material I containing the hypoeutectic aluminum alloy composition, which is shown in Table 3, is in a stirred casting process produced and had a diameter of 76 mm and a length of 100 mm.

The 15A FIG. 12 is a micrograph showing the metallographic structure of an outer layer portion of the aluminum alloy material I, and FIGS 15B is a reproduction of an in 15A shown essential part. In this case, the average column length (block length) L of the dendrites is 172 μm. The area rate a of the α-Al crystals in the outer layer portion is 81% and the area rate b of the α-Al crystals in the main body portion is 76%.

The Aluminum alloy material I is disposed in the induction heating furnace and then an induction heating under conditions one Frequency f of 1 kHz (constant) and an excitation time of 7 minutes been subjected (90% issue for the first 3 minutes, issue 50% for the next 1 minute and spending 37% for the last 3 minutes).

In this case, the electrical resistance of the outer layer portion is less than that Because of the fact that the area rate a of the α-Al crystals in the outer layer portion is higher than the area rate b of the α-Al crystals in the main body portion and the α-Al crystal has good conductivity. Therefore, a considerable skin effect has occurred in the outer layer portion, causing the temperature of the outer layer portion to be preferably increased with respect to the main body portion, so that the outer layer portion has assumed a semi-molten state with solid and liquid phases coexistent therewith , Subsequent induction heating caused the temperature of the main body portion to be raised so that it also assumed a semi-molten state with solid and liquid phases coexistent therewith.

In this manner, the aluminum alloy material has been heated to 575 ° C, which is a pourable temperature. Then, the metallographic structure in the semi-molten state has been fixed by a quenching method, and the metallographic structure of the outer layer portion has been investigated, resulting in the in 16 results shown.

The 16 Fig. 10 is a micrograph showing the metallographic structure of the outer layer portion. You can go out 16 recognize that the dendrites in the outer layer portion have been transformed by the semi-melting into spherical solid phases. In this case, a mean diameter D of the solid phases of the α-Al crystals is 200 μm.

Of the Main body portion also has a fine spherical Structure on, for the same reason as described above.

Then the mold temperature in the Preßgießeinrichtung 1 , what a 9 has been set to 250 ° C and the semi-molten alloy material I (by the reference numeral 5 when heated) is in the chamber 6 in the Preßgießeinrichtung 1 been arranged. The plunger 9 has been actuated to the semi-molten aluminum alloy material I in the cavity 4 invite. In this case, the pressure for charging the semi-molten aluminum alloy material I was 8 MPa. Then it is on the semi-molten aluminum alloy material I, which in the cavity 4 was filled, a pressing pressure was exerted by the plunger 9 has been held at a stroke end, whereby the aluminum alloy material I has been solidified under such a pressure to provide the aluminum alloy casting product I.

The 17 FIG. 13 is a micrograph showing the metallographic structure of the aluminum alloy casting I. FIG. You can go out 17 recognize that the metallographic structure is homogeneous.

This is due to the fact that the casting material passed through the passage in a solid state is, without separation of the solid and liquid phases from each other, when it was loaded into the cavity.

(Example 2)

One Aluminum alloy material II, which is shown in Table 3 had hypoeutectic aluminum alloy composition is in a stirred casting process produced and had a diameter of 76 mm and a length of 100 mm.

The 18A FIG. 12 is a photomicrograph showing the metallographic structure of an outer layer portion of the aluminum alloy material II, and FIG 18B is a reproduction of an in 18A shown essential part. In this case, a mean column length L of the dendrites is equal to 216 μm. The area rate a of the α-Al crystals in the outer layer portion is 82%, and the area rate b of the α-Al crystals in the main body portion is 75%.

The aluminum alloy material II was placed in the induction heating furnace and then subjected to induction heating under the same conditions as in Example 1. Then, the aluminum alloy material II was heated to 575 ° C, at which temperature the material II was in a semi-molten state with coexistent solid and liquid phases, and which temperature was a pourable temperature. Thereafter, the metallographic structure in the semi-molten state has been fixed by a quenching method, and the metallographic structure of the outer layer portion has been investigated, resulting in the in-mold 19 shown result.

The 19 Fig. 10 is a micrograph showing the metallographic structure of the outer layer portion. You can go out 19 recognize that the dendrites in the outer layer portion have been transformed by the semi-melting into spherical solid phases. In this case, a mean diameter D of the solid phases of the α-Al crystals is equal to 230 μm.

Then, using the semi-molten aluminum alloy material II after it has been heated, and using the in 9 shown Preßgießeinrichtung 1 an aluminum alloy casting II was prepared by the same casting as in Example 1. In this case, the pressure for charging the semi-molten aluminum alloy material II was 14 MPa.

The 20A and 20B are photomicrographs respectively showing the metallographic structures of various sections of the aluminum alloy casting II. As from the comparison of 20A and 20B As can be seen, the metallographic structures are not homogeneous.

This is because, as the semi-molten aluminum alloy material II in the Cavity has been loaded, clogging the passage (with a diameter of 10 mm) has occurred with the material II, which has led to a separation of the solid and liquid phases from each other, since the mean diameter D of the solid phases in the outer layer portion 230 μm in size.

From the comparison of 17 with the 20A and 20B it can be seen that the average diameter D of the spherical solid phases in the outer layer portion of the semi-molten aluminum alloy material in a solid / liquid phase coexistence state is desirably in the range of D ≦ 200 μm.

Then are test pieces from the aluminum alloy castings I and II have been prepared in Examples 1 and 2 and a Subjected to T6 treatment, according to the previously described, and then subjected to a tensile test, resulting in the in Table 7 results shown Has. In Table 7, test pieces I and II correspond to the aluminum alloy castings I or II.

Table 7

As From Table 7, the test piece I in Example 1 has higher strength and a greater ductility than those of the test piece II in Example 2. This is due to the difference of metallographic Structures of aluminum alloy castings I and II and originally on the difference between the mean diameters D of the fixed Phases in the outer layer sections of semi-molten casting materials.

In summary the invention a semi-molten casting material, in the solid and liquid Phases coexist.

A plurality of composite solid phases having liquid and solid phase portions and a plurality of single solid phases exist as the solid phases in an outer layer portion of the semi-molten casting material. When the sectional area of the solid phase area is represented by A, and when the sectional area of the solid phase area in one of the composite solid phases is represented by B, the liquid inclusion rate P of the composite solid phase is defined as P = {B / (A + B)} × 100 (%). The liquid inclusion rate P of the single solid phase is 0 (%). When two groups of a class of the solid phase are selected, for example, by first and second straight lines to include a plurality of solid phases, averages M ₁ and M _{2 are} the liquid inclusion rates of, for example, six solid phases in the first and second Groups represented by M ₁ = (P ₁ + P ₂ ... + P ₅ + P ₆ ) / 6 and M ₂ = (P ₄ + P ₇ ... + P ₁₀ + P ₁₁ ) / 6, and an average M _{M of} the mean values M ₁ and M ₂ is set in the range of M _M ≥ 20%. Thus, it is possible to prevent the leakage of the liquid phases from the outer layer portion in the semi-molten thixocasting molding material.

Claims (4)

A semi-molten casting material for thixocasting having a main body portion and an outer layer portion and having a hypoeutectic aluminum alloy composition and solid and liquid phases coexistent therewith, wherein the material comprises a plurality of composite solid phases each having a liquid phase region and a liquid phase region and a plurality of single solid phases having no liquid phase region, wherein the composite solid phases and the individual solid phases are mixed as the solid phases in an outer layer portion of the semi-molten casting material, and wherein when a liquid phase inclusion rate P of the composite solid phase is defined as P = {B / (A + B)} × 100 (%), where A is a sectional area of the solid phase area and B is a sectional area of the liquid phase area, and wherein the liquid phase ssiphase inclusion rate P of the single solid phase is defined as P = 0 (%), and when a number N of groups of a class of the solid phases in the outer layer portion is selected to include a plurality of the solid phases, averages M ₁ to M _{N of} the liquid phase inclusion rates P ₁ , P ₂ ... P _n-1 and P _{n of} a number n of solid phases are calculated for first through N-th groups and are represented by M ₁ = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n to M _N = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n and a total average M _M (= (M ₁ + M ₂ . .. + M _N-1 + M _N ) / N) of the mean values M ₁ to M _{N is set} in the range of M _M ≥ 20%, from a starting thixocasting material having an outer layer portion with dendrites around a main body portion, wherein the area rate of the α-Al crystals in the outer layer portion is higher than the area rate of the α-Al crystals in the main body portion, obtained by exposing the Thixogießmaterials one r heat treatment to produce the semi-molten thixocasting material having coexistent solid and liquid phases, wherein the dendrites are transformed into spherical solid phases to bring the outer layer portion into a semi-molten state by raising the temperature of the outer layer portion with respect to Main body section, wherein the heat treatment comprises two successive heating steps by induction heating and in the first heating step, a frequency f ₁ with 0.8 Hz <f ₁ ≤ 50 kHz and applied in the second heating step, a frequency f ₂ with 0.8 kHz <f ₂ ≤ 5 kHz is under the condition that f ₁ > f ₂ . A semi-molten casting material for thixocasting having a main body portion and an outer layer portion and having a hypoeutectic aluminum alloy composition and solid and liquid phases coexistent therewith, wherein the solid phases existing in the outer layer portion of the casting material are a plurality of composite solid phases, each having a liquid phase region and a solid phase region surrounding the liquid phase region, and wherein when a liquid phase inclusion rate P of the composite solid phases is defined as P = {B / (A + B)} × 100 (%), where A is a sectional area of the solid phase region and B is a sectional area of the liquid phase region, and when a number N of groups of a compound of the composite solid phases in the outer layer portion is selected to comprise a plurality of the composite solid phases, averages M ₁ to M _N of Liquid phase inclusion rates P ₁ , P ₂ , ... P _n-1 , and P _{n of} a number n of the composite solid phases are calculated for each first through N-th groups and are represented by M ₁ = (P ₁ + P _2. + P _n-1 + P _n ) / n to M _N = (P ₁ + P ₂ ... + P _n-1 + P _n ) / n and a total average M _M (= (M ₁ + M ₂ ... + M _N-1 , + M _N ) / N) of the average values M ₁ to M _{N is set} in the range of M _M ≥ 20%, from a starting thixocasting material having an outer layer portion with dendrites around a main body portion wherein the area rate of the α-Al crystals in the outer layer portion is higher than the area rate of the α-Al crystals in the main body portion obtained by exposing the thixocasting material to heat treatment to the semi-molten thixocasting material having coexistent solid and liquid phases in which the dendrites are transformed into spherical solid phases in order to convert the outer layer segment into a semi-solid phase. the heat treatment comprises two successive heating steps by induction heating and in the first heating step a frequency f _{1 of} 0.8 Hz <f ₁ ≤ 50 kHz and in the second heating step a frequency f ₂ with 0.8 kHz <f ₂ ≤ 5 kHz is applied under the condition that f ₁ > f ₂ . Semi-molten thixocasting casting material according to claim 1 or 2, characterized in that the casting material is spherical solid Phases in the outer layer section in the semi-molten state with a mean diameter D the spherical one Has phases in the range of D ≤ 200 microns. Semi-molten thixocasting casting material according to one of the preceding claims, characterized in that in the area rate of α-Al in the outer layer section is represented by a% and the area rate of α-Al in the main body portion is represented by b% and a difference a-b between the two area rates is in the range of 5% ≤ a-b ≤ 15%.